Meaning "course or method of action" is from mid-14c.; sense of "continuous series of actions meant to accomplish some result" (the main modern sense) is from 1620s. Legal sense of "course of action of a suit at law" is attested from early 14c.

1530s, "begin legal action against," from Middle French processer "to prosecute," from proces (see process (n.)). Meaning "prepare by special process" is from 1881, from the noun in English. Of persons, "to register and examine," by 1935. Related: Processed; processing.